Acids, Bases and Buffers

Question 1

what is a salt?

Answer 1

A compound formed when the hydrogen ion from an acid is replaced by a metal ion or ammonium ion

Question 2

what is an alkali?

Answer 2

A soluble base which dissolves in water to release OH- ions

Question 3

what do acids release in water?

Answer 3

H+ ions

Question 4

what do alkalis release in water?

Answer 4

OH- ions

Question 5

What is a Brønsted–Lowry acid

Answer 5

proton (H+ ion) donator

Question 6

What is a Brønsted–Lowry base

Answer 6

proton (H+ ion) acceptor

Question 7

What is a conjucate acid/base pair?

Answer 7

Pair of species which differ by the loss or gain of an electron

Question 8

what is Kw?

Answer 8

The ionic product of water

Question 9

what is the equation for Kw?

Answer 9

Kw = [H+][OH-]

Question 10

What is the numerical value of Kw?

Answer 10

1.00 x 10^-14 mol² dm^-6

Question 11

As temperature increases, what happens to kw?

Answer 11

kw increases

Question 12

what is the relationship of [OH-], [H+] and Kw in a neutral solution

Answer 12

[OH-] = [H+]

Kw = [H+]²

[H+] = √Kw

=√1 x 10^-14

Question 13

what is the simple pH equation?

Answer 13

pH = -log [H+]

Question 14

what is the simple [H+] equation?

Answer 14

[H+] = 10^-pH

Question 15

what is the simple equation for pOH?

Answer 15

pH = -log [OH-]

Question 16

What is the simple equation for [OH-]?

Answer 16

[OH-] = 10^-pOH

Question 17

what is a strong acid?

Answer 17

An acid which completely dissociates in water to form H+ ions.

Question 18

what is a weak acid?

Answer 18

An acid which partially dissociates in water to form H+ ions.

Question 19

what is a strong base?

Answer 19

A base which completely dissociates in water to form OH- ions.

Question 20

what is a weak base?

Answer 20

A base which partially dissociates in water to form OH- ions.

Question 21

Define the Acid dissociation constant

Answer 21

Question 22

what is the Ka like in weak acids?

Answer 22

Fewer ion ∴ smaller Ka

Question 23

what is the Ka like in strong acids?

Answer 23

more ion ∴ larger Ka

Question 24

what does Ka measure?

Answer 24

The extent of ionisation

Question 25

how do you calculate pka from Ka?

Answer 25

-log(Ka)

Question 26

How do you calculate Ka from pKa?

Answer 26

10^-pKa

Question 27

what is the Ka and pKa like in strong acids?

Answer 27

high Ka low pKa

Question 28

what is the Ka and pKa like in weak acids?

Answer 28

low Ka high pKa

Question 29

what do we use to compare the strengths of weak acids?

Answer 29

Ka

Question 30

how to work out pH of strong acids

Answer 30

conc of acid = [H+] pH = -log [H+]

Question 31

how to work out conc of strong acids

Answer 31

[H+] = 10^-pH [H+] = Conc of acid

Question 32

how to work out pH of stong bases

Answer 32

Kw = [H+][OH-] [H+] = Kw/[OH-] Kw = 1.00 x 10^-14 [H+] = 1.00 x 10^-14/[OH-] pH = -log [H+]

Question 33

how to work out conc of strong base

Answer 33

[H+] = 10^-pH Kw = [H+][OH-] [OH-] = Kw/[H+] Kw = 1.00 x 10-14 [OH-] = 1.00 x 10-14/[H+]

Question 34

How to calculate pH of weak acid

Answer 34

Ka = [H+]² / [HA] [H+]² = Ka x [HA] [H+] = √Ka x [HA]

Question 35

How to calculate conc of weak acid

Answer 35

[H+] = 10^-pH Ka = [H+]²/[HA]

Question 36

Ka and pKa circle

Answer 36

Question 37

[H+] and pH circle

Answer 37

Question 38

what is a buffer solution?

Answer 38

a solution which minimises changes in pH when small amounts of acid or base are added

Question 39

what is the order of words you need to know about buffers when pH falls?

Answer 39

1. [H+] rises (H+ + A- ---\> HA) [H+] decreases equilibrium moves to the acid to decrease [H+]

Question 40

what is the order of words you need to know about buffers when pH rises?

Answer 40

[OH-] increases Neutralisation of OH- (H+ + OH- -----\> H2O) the equilibrium move to the products to increase [H+] Acid dissociates to oppose [H+] decrease

Question 41

what is buffer equation?

Answer 41

Question 43

Answer 43

Question 44

Answer 44

Question 45

What are the approximations in calculating weak acids?

Answer 45

1. The dissociation of water is negligible (Doesnt work for very weak acids) [H+] ~ [A-] 2. the conc of acid is much greater than the conc of H+ (this works for weak acids with a low Ka, but as strenth increases this doesnt work)